City trees constitute perhaps the single most important green
structure in addition to open green space in cities. City trees
potentially provide a bundle of ecosystem services. Oslo Municipality
has a strategy to replace every municipal tree felled within the built
zone with at least one new one. Damage to trees on municipal land is
subject to a fine and a compensation claim using an established
liability assessment model for city trees.

VAT03-BBN

This liability or compensation value for city trees is calculated
using the VAT03 assessment model developed by [Randrup, 2005] and adapted to a BBN by [Barton et al, 2015]. The VAT03 assessment model is
based on the replacement cost of a city tree, including purchase and
planting costs. This base value is then adjusted for the tree.s
structural health and for its qualities in a neighbourhood context,
including adaptation and contribution to its local
environmental. Environmental qualities include aesthetics, noise and
pollution reduction, in other words several regulating ecosystem
services. An overview of the VAT03 model structure is provided in
Figure 1.

The tree valuation model is based on [Randrup,
2005] adjusted to the Oslo case study #3.

Aggregation

[Barton et al, 2015] used the VAT03-BBN to calculate the aggregate
expected compensation value of all city trees taller than 5 meters in
Oslo.s built zone.

Property rights (work in progress)

There is currently no environmental liability on trees on private land
from a legal point of view. However, there is no reason to believe
that trees have less regulating functions just because they are
located on private land. Private land might be correlated with other
spatial factors that differentiate demand for a tree.s regulating
services. As a precautionary principle one could argue that also
trees on private land should have environmental liability because a
number of the regulating and cultural ecosystem services are public
goods. With this in mind the VAT03-BBN may be used to answer the
question, what would be the liability value of any city tree in the
built zone - whether on public or private land - if it were assessed
according to VAT03?

Tree density (work in progress)

Another limitation of VAT03 to be addressed in further model
development concerns the value of individual trees in forest stands
within or bordering the city built zone. The liability values
calculated by the municipality using VAT03 for individual trees have
been challenged in cases were trees are in stands. As a demo we show
how the VAT03 could scale between individual trees valued at full
VAT03 liability value and trees in forest stands assessed only for
timber value. In the demo the model scales tree compensation value
according to the tree density in the neighbourhood of the tree in
question.

Map Interpretation

Each blue element (polygon) on the map represents a tree. When the
left mouse button is pressed on a blue element, the value of the
selected tree is computed and added to a layer on top of the blue
placemarks. This layer has a polygon for the selected element with
color green. The intensity of the green color is determined by the
expected tree compensation value.

That is, the intensity of the chloropleth color is determined by the
expected tree compentation value (normalized using division by 70000). An
expected value of zero produce a transparent placemark where as the
value one (or above) produce a placemark with color green at full
intensity.

Full compatibility of the maps can be viewed with IE11 or Firefox 33.

Model Usage

Below are some HUGIN widgets for interacting with the model shown on
the right (click on the probability bar to instantiate a node or
remove evidence). Notice that Dashboard contains a lot of variables
that can be instantiated.

Associated with each tree is information on properties of the
tree. The tree compensation value is computed by propagating this
information in the Bayesian network shown in the figure above. The
intensity of the green color is determined by expected tree
compensation value. The more intense the color is, the higher the
expected value of the tree is.

The Compute button computes the sum of the expected values of the
selected trees on the map, i.e., the trees selected so far. The set of
selected trees can be reset (and all evidence removed from the models)
by presseing Reset.

The Save data button allows the user to download a file with the
information entered using the widgets for a single tree.